Space vehicles require that certain parameters be sensed and monitored to detect impending faults, to detect and respond to certain conditions, and to maintain desired environments for operating equipment. For example, typical space borne electronic systems require the temperature to be sensed at many points so that the effects of temperature can be compensated for. Sensors for temperature, along with pressure and other parameters are, therefore, positioned at various locations within a space vehicle. The sensors are linked to a controller, such as a computer, for periodic reading and recording of measured values. The sensors are often interfaced to address circuitry which is networked to the computer so that the sensors can be read in an orderly and efficient manner.
With all types of mobile platforms, it is always desirable to reduce weight to maximize propulsion efficiencies and even more so in relation to space vehicles. A typical space payload may have 600 to 800 pounds (about 270 to 360 kg) of sensor interconnect cables, with each cable having 50 to 60 sensing devices connected thereto, such as for measurement of temperature, pressure, electrical parameters, mechanical parameters, or the like.
Radio frequency identification (RFID) systems are used in a variety of applications, ranging from warehouse inventory control and container tracking, through automatic toll payment, to automatic supermarket cashier applications. In a typical RFID system, an RF transponder is attached to, or incorporated into, a tracked object. RF transmissions between an interrogation device or a reader and the transponder are used for identifying or controlling the object, reading data, writing data or otherwise communicating with the transponder.
RF transponders are commonly classified in terms of the use they make of an internal power source. A passive transponder has no internal power source and uses the energy of the RF radiation transmitted by the reader, referred to as interrogation radiation or a query signal, for powering the transponder circuitry and for transmitting response radiation back to the reader. The response radiation or reply signal typically comprises information, such as an identification number, transmitted from the transponder to the reader. An active transponder comprises an internal power source that is used for both powering the transponder and for generating the RF energy required for transmitting the response radiation.
Known types of passive transponders are often not suitable for use in space platforms because of limited range, high power consumption, or both. Additionally, space vehicles and equipment therein are often highly reflective internally, creating multi-path problems which must be resolved.